The disclosures of Japanese Patent Application No. 2001-229681 filed on Jul. 30, 2001 including the specification, drawings and abstract, are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a dynamic damper which is adapted to be mounted on a steering column or a steering wheel of an automotive vehicle for the purpose of damping or attenuating vibrations excited in a steering wheel.
2. Description of the Related Art
A steering wheel of an automotive vehicle is generally fixed to a free end of a longitudinal steering column that is supported by the vehicle at a bound end thereof. Therefore, the steering wheel is prone to be subjected to vibrations applied thereto in a direction perpendicular to an axial direction of the steering column. Further, a driver of the vehicle almost always handles directly the steering wheel during driving the vehicle, and eventually is able to sensitively feel minute vibrations excited in the steering wheel. Since the vibrations excited in the steering wheel greatly impact on a riding comfort of the vehicle as felt by the driver, there has been a great regard for absorbing the vibrations excited in the steering wheel.
In an attempt to damp or attenuate vibrations excited in the steering wheel, a dynamic damper, which includes a mass member and a spring member for elastically supporting the mass member, has been mounted on the steering wheel or other members of the steering system, thereby providing a secondary vibration system for the steering system as a primary vibration system. A natural frequency of the secondary vibration system is tuned to a natural frequency of the steering system, so that the vibrations excited in the steering wheel may be damped.
Keeping pace with recent advancement in recognition of safety and recent tendency of upgrading automotive vehicles, a telescopic steering column has been developed in order to allow a driver to adjust a position of the steering wheel in a longitudinal direction of the vehicle, depending upon his or her body-build or affinity.
An extensive study of the dynamic damper for use in the steering system conducted by the present inventor has revealed the fact that the conventional dynamic damper is not able to exhibit a desired damping effect for vibrations excited in a steering system equipped with the telescopic steering column. Described in detail, such a steering system experiences a change of the axial length of the steering column upon adjusting the position of the steering wheel supported by the steering column. This causes a relatively large amount of change in the spring constant of the steering column for supporting the steering wheel, thereby inevitably changing a natural frequency of the steering wheel supported by the steering column over a wide frequency range. Therefore, the conventional dynamic damper that is tuned to a specific frequency range may suffer from deterioration in its damping effect depending upon the selected position of the steering wheel. That is, the conventional dynamic damper is incapable of stably exhibiting a desired damping effect with respect to vibrations excited in the telescopic steering column.
To cope with this conventional problem, it has been proposed to install on the telescopic steering column a plurality of dynamic dampers that are tuned to different frequency ranges. However, since the axial length of the telescopic steering column may vary among a great number of possible values, or may be continuously changed over a given axial distance, it is not practical to install on the telescopic steering column a great number of dynamic dampers that are tuned to a great number of possible natural frequencies of the steering wheel, respectively.
It is therefore one object of this invention to provide a dynamic damping device for use in a steering system equipped with a telescopic steering column, which is novel in construction, and which is capable of stably exhibiting an excellent vibration damping effect with respect to vibrations excited in the steering wheel while assuring a reduced number of dynamic dampers to be mounted on the steering system.
The above and/or other objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principal of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A dynamic damping device for use in a steering system equipped with a telescopic steering column of an automotive vehicle, and adapted to be mounted on a steering column and/or a steering wheel of the steering system for damping vibrations excited in the steering wheel, the dynamic damping device comprising: (a) a plurality of dynamic dampers each including a mass member and a spring member for elastically supporting the mass member with respect to the steering column or the steering wheel, the plurality of dynamic dampers being independent of each other, wherein the plurality of dynamic dampers have respective natural frequencies that are arranged such that at least two of the natural frequencies of the plurality of dynamic dampers are tuned respectively to a higher and a lower frequency range in relation to a central value of a range of variation in a natural frequency of the steering wheel due to an expansion or contraction of the telescopic steering column, and held within the range of vibration in the natural frequency of the steering wheel, and such that differences between adjacent ones of the natural frequencies of the plurality of dynamic dampers are held within 10-40% of the central value of the range of vibration in the natural frequency of the steering wheel.
According to this mode of the invention, the dynamic damping device includes the plurality of dynamic dampers whose natural frequencies are uniquely tuned as described above. This arrangement enables the dynamic damping device to damp vibrations excited in the steering wheel with efficiency and stability with the help of a fewer number of dynamic dampers, even when the natural frequency of the steering wheel is changed due to a positioning operation of the steering wheel.
If the natural frequencies of the plurality of dynamic dampers are tuned to one of the higher and lower frequency ranges in relation to the central value of the range of vibration in the natural frequency of the steering wheel, the dynamic damping device may suffer from difficulty in exhibiting a desired damping effect with respect to vibrations excited in the steering wheel whose frequencies corresponding to the other one of the higher and lower frequency ranges. In addition, if the differences between the adjacent ones of the natural frequencies of the plurality of dynamic dampers are deviate from 10-40% of the central value of the range of vibration in the natural frequency of the steering wheel, the dynamic damping device become ineffective with respect to a frequency range within the range of vibration in the natural frequency of the steering wheel. As a result, the vibration condition of the steering wheel may be deteriorated depending upon the selected position of the steering wheel. Described in detail, if the difference between the adjacent ones of the natural frequencies of the dynamic dampers is made smaller than 10% of the central value of the possible natural frequency range of the steering wheel, damping effects of these two dynamic dampers overlap with each other in terms of frequency, and the two dynamic dampers cooperate to exhibit a single damping effect that is similar to the damping effects exhibited by the dynamic damper having single mass member. Accordingly, the dynamic damping device become incapable of exhibiting a desired damping effect with respect to vibrations over a wide frequency range. On the other hand, if the difference between the adjacent ones of the natural frequencies of the dynamic dampers is made larger than 40% of the central value of the possible natural frequency range of the steering wheel, the damping effects exhibited by the two dynamic dampers too strongly show independence of each other in terms of their frequency characteristics to prevent deterioration of damping effects at a frequency range interposed between the adjacent natural frequencies of the two dynamic dampers. Consequently, the dynamic damping device is less likely to exhibit an excellent damping effect for a wide frequency range of input vibrations.
Namely, in the dynamic damping device for use in a steering system according to the present invention, the adjacent natural frequencies of the two dynamic dampers are relatively arranged to be held within a range of 10-40% of the central value of the variation range of the natural frequency of the steering wheel. This arrangement makes it possible to improve damping effects at the frequency range interposed between the natural frequencies of the two dynamic dampers, thereby substantially connecting or expanding frequency ranges in which the dynamic dampers can exhibit excellent damping effects. Therefore, the present dynamic damping device is suitably applicable to damp vibrations excited in the steering wheel whose natural frequencies varies due to the expansion or contraction of the telescopic steering column, and makes it possible to deal with the entire range of variation of the natural frequency of the steering wheel with a generally fewer number of dynamic dampers. Thus, the dynamic damping device of the present invention is able to exhibit a desired damping effect with stability regardless of position of the steering wheel in the central axis of the steering column, thus making it possible to provide a steering mechanism equipped with a telescopic steering column for an automotive vehicle, which assures a good riding comfort of the vehicle as felt by a driver of the vehicle.
In this mode of the present invention, the telescopic steering column should be interpreted to mean any steering column whose axial length is variable to be comply with the driver""s body-build or affinity, and has a variety of structures, without any specific limitation. According to the present mode of the invention, the plurality of dynamic dampers may be desirably tuned so long as at least two of the natural frequencies of the plurality of dynamic dampers are tuned to a higher and a lower frequency range in relation to the central value of the range of variation in the natural frequency of the steering wheel, and held within the range of vibration in the natural frequency of the steering wheel. In the case where more than three dynamic dampers are employed, for example, one of the three dynamic dampers may be tuned to the central value of the variation range of the natural frequency of the steering wheel, or alternatively may be tuned to a frequency range that is located outside of the variation range of the natural frequency of the steering wheel.
(2) A dynamic damping device according to the above-indicated mode (1), wherein the natural frequencies of the plurality of dynamic dampers are all held within the range of variation in the natural frequency of the steering wheel due to an expansion or contraction of the telescopic steering column. This arrangement makes it possible to efficiently cover the range of variation of the natural frequency of the steering wheel with a fewer number of dynamic dampers. Accordingly, the dynamic damping device is able to exhibit a desired damping effect with respect to vibrations excited in the steering wheel whose natural frequencies varies as a result of the expansion or contraction of the telescopic steering column.
(3) A dynamic damping device according to the above indicated mode (1) or (2), further comprising a bracket adapted to be fixed to the steering column or the steering wheel of the steering system, and supporting the plurality of dynamic dampers. According to this mode of the invention, the plurality of dynamic dampers can be fixed to the bracket in advance, thereby improving efficiency in installing the plurality of dynamic dampers on the steering column or the steering wheel.
(4) A dynamic damping device according to any one of the above-indicated modes (1)-(3), wherein the spring member of each of the plurality of dynamic dampers comprises an elastic support member adapted to undergo shear deformation in a direction perpendicular to a central axis of the steering column or the steering wheel. In this mode of the invention, since the spring member is constituted by the elastic support member formed of a rubber elastic body, thereby effectively obtaining damping coefficient of the dynamic dampers. In addition, the elastic support member undergoes shear deformation in the vibration input direction, thereby exhibiting a relatively low spring constant. This makes it possible to easily tune the natural frequency of each of the dynamic dampers to be held within the range of variation of the natural frequency of the steering wheel, while avoiding or minimizing an enlargement of the mass member and deterioration of the durability of the spring member.
(5) A dynamic damper according to the above-indicated mode (4), wherein the elastic support member of each of the plurality of dynamic dampers has a circular shape in cross-section in the direction perpendicular to the central axis of the steering column or the steering wheel. This arrangement is effective to prevent or minimize undesirable changes in the spring constant of each spring member and in the natural frequency of each dynamic damper, if a vibration input direction with respect to the spring member changes due to the turning of the steering wheel, for example. Thus, the dynamic damping device of this mode of the invention is capable of exhibiting an excellent vibration damping effect with high stability, with respect to vibrations applied thereto in different radial directions.
(6) A dynamic damper according to the above-indicated mode (4) or (5), wherein each of the plurality of dynamic dampers is arranged such that the elastic support member has a principal elastic axis that approximately conform with a principal inertia axis of the mass member in a direction approximately parallel to the central axis of the steering column or the steering wheel. In this mode of the invention, the dynamic damping device is able to stabilize vibration attitude or condition of the mass members upon application of the vibrational load in radial directions perpendicular to the central axis of the steering wheel, making it possible for the dynamic damping device to exhibit a desired vibration damping effect in a more effective and stabile manner.
In this mode (6) of the invention, an elastic center of the elastic support member may preferably be located closer to a center of gravity of the mass member in each dynamic damper, for thereby further stabilizing vibration attitude of the mass members. Namely, this arrangement is effective to prevent or minimize a rotative or a tilting motion of the mass members when the dynamic dampers are subjected to the vibration in the direction perpendicular to the central axis of the steering wheel, permitting the dynamic damping device to exhibit a desired vibration damping effect in a further effective and stable manner. In order to locate the elastic center of the elastic support member close to the center of gravity of the mass member, each dynamic damper may have a variety of configuration. For instance, the mass member may have a cylindrical shape and is disposed radially outwardly of the elastic support member so as to protrude toward the side of the bracket, so that the elastic center of the elastic support member is located close to the center of gravity of the mass member effectively.